Patent literature 1: JP2009-93343A
Recently, a technology by which information with respect to a travelling condition of an vehicle outside a subject vehicle or a road situation is obtained using a vehicle-vehicle communication or a road-vehicle communication is proposed (for example, referring to patent literature 1).
For confirming whether a communication apparatus provided to a subject vehicle correctly outputs a radio wave or for confirming whether a transmission function is correctly performed, a method by which it is determined that the communication apparatus of the subject vehicle functions correctly when the communication apparatus broadcasts a response request to a surrounding communication apparatus and the communication apparatus receives a response from the surrounding communication apparatus is known.
The inventors of the present application have found the following. When the above method may be performed in a vehicle-vehicle communication, a lot of responses may occur and a communication to be originally performed may be prevented according to density of surrounding communication apparatus.